Putin said that Russia successfully tested the missile in 2017, which besides sounding incredibly dangerous as it's an untested flying nuclear reactor, had not been reported by any news outlets in or outside the country.

But on Thursday, Fox News's Lucas Tomlinson quoted US officials as saying the weapon was not yet operational, and that the test had failed.

Though Putin said, and later tweeted, that the missile worked, he was only able to show a computer animation of the missile during his speech. In fact, all the missile systems he talked up during his speech were demonstrated with computer animations, and not actual footage.

In any case, Russia having or not having a nuclear-powered cruise missile doesn't really alter the balance of power that much.

The US relies on the doctrine of "mutually assured deterrence," or having Putin rest with the knowledge that if he ever did fire a nuclear weapon at the US or one of its allies, US nuclear missiles would find him too.